"Invalid URL" alert appears when adding multiple instances of Web Content tool

The "Alert: Invalid URL" message appears when users have not entered any text into the "Source" box and they choose to add more instances of the Web Content tool.

The alert appears because it seems to be checking the Source box for the first instance and reads that there's nothing there, so the alert is thrown. This isn't very helpful for users, however, especially if they had selected the option to add 3 instances of the tool and pressed "Continue" without providing addresses. The alert stacks on top of itself.

Steps to reproduce:

1. Go to Site Info
2. Go to Manage Tools
3. Select Web Content tool to add and press continue
4. In the "More Web Content Tools?" section, choose 1 more.
5. "Invalid URL" alert will appear

Ideally, the site would recognize that these boxes are simply empty and proceed to add the tools that DO have valid URLs while deleting the empty instances.

Video demonstrating the issue: http://www.screencast.com/t/n9ARNXKuD
Testing was done on Nightly 11x Maintenance Branch on Oracle.